Expandable ablation burr

ABSTRACT

An atherectomy burr has an operating diameter that is larger than the diameter of a catheter in which the burr is routed. The burr may include an expandable polymeric balloon having a partially abrasive exterior surface. The maximum expansion of the burr is controlled by an expansion mechanism. Various mechanisms are disclosed for controlling the maximum diameter of the burr thus preventing the burr from over expanding. In addition, the present invention includes systems that are pulled proximally to remove portions of a lesion located in a patient&#39;s vasculature. The system includes an ablation burr that has abrasive disposed on the proximal end. The burr may create a seal when expanded to block the ablated particulate so that an aspiration system can remove the particulate from the vasculature. Alternatively, the burr system may include a self expanding seal that is deployed out of the aspiration sheath.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/629,771filed Jul. 31, 2000, now U.S. Pat. No. 6,685,718, which is acontinuation-in-part of application Ser. No. 09/178,449, filed Oct. 23,1998, now U.S. Pat. No. 6,096,054, which in turn claims benefit fromU.S. Provisional Application No. 60/076,963, filed Mar. 5, 1998 all ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to medical devices in general, and inparticular to atherectomy devices for removing occluding material from apatient's blood vessels.

BACKGROUND OF THE INVENTION

Arteriosclerosis is a common vascular disease in which a patient's bloodvessels become hardened and blocked by plaque or clots that impede bloodflow. Left untreated, this condition is a major contributing factor tothe occurrence of high blood pressure, strokes and cardiac arrest.

To treat arteriosclerosis, many invasive and non-invasive techniqueshave been developed. For example, cardiac bypass surgery is now acommonly performed procedure whereby an occluded cardiac artery isbypassed with a segment of a healthy blood vessel that is obtained fromelsewhere in the body. While this procedure is generally successful, itis fairly traumatic because the entire chest cavity must be opened toaccess the occluded vessel. Therefore, the procedure is not generallyperformed on elderly or relatively frail patients.

One example of a promising minimally invasive technique that can beperformed on a greater number of patients is to remove the occludingmaterial from a patient's vessel in an atherectomy procedure. To performthis procedure, a guide catheter is typically inserted into thepatient's femoral artery and advanced until the distal end of the guidecatheter is located in the patient's coronary ostium. A guide wire isthen inserted through the guide catheter and traversed into the coronaryarteries and past the occluded material to be treated. Then, asdescribed in U.S. Pat. No. 4,990,134, issued to Auth, an atherectomycatheter having a small abrasive burr is advanced through the guidecatheter and over the guide wire to the point of the occlusion. The burris then rotated at high speed and passed through the occlusion to removeparticles that are sufficiently small such that they will not occlude inthe distal vasculature. As the burr removes the occlusion, a largerlumen is created in the vessel and blood flow is restored.

It is well recognized that the risk of certain patient complicationsincreases with the size of the guide catheter through which minimallyinvasive devices are routed. Larger guide catheters require largeraccess holes in the femoral artery, creating the potential for patientcomplications, such as the sealing of the puncture site after completionof the procedure. Therefore, physicians generally wish to utilize thesmallest possible guide catheter during a procedure. However, thesmaller size guide catheters can only accommodate corresponding smallersize ablation burrs. Therefore, if a large vessel is to be treated, alarger burr and corresponding larger guide catheter must be used tosuccessfully remove all of the occlusion from the patient's vessel.

In addition, it has also been discovered that when performing anatherectomy procedure as described earlier, it has been beneficial toremove only a small amount of the occlusion at a time. Therefore,currently many procedures are performed using multiple passes throughthe occlusion with different sized ablation burrs. While theseprocedures have proven effective, the use of multiple devices for asingle procedure adds both time and cost to the procedure.

Given the disadvantages of the existing atherectomy devices, there is aneed for an atherectomy device that can treat different size vesselswhile being traversed through a small guide catheter.

SUMMARY OF THE INVENTION

To eliminate the need for a physician to utilize larger guide cathetersin order to route a larger diameter ablation burr in a patient, thepresent invention comprises an expandable ablation burr. The ablateddiameter preferably has a diameter that exceeds the diameter of a guidecatheter through which the burr is routed.

According to one embodiment of the invention, the ablation burr includesa polymeric balloon that expands as the burr is rotated. A portion ofthe balloon is coated with an abrasive such that the balloon will ablatean occlusion as the burr is rotated and advanced through a vessel.

According to another aspect of the present invention, the expandableablation burr includes an expansion control mechanism which allows theultimate or final outer diameter of the burr to be predetermined andcontrolled to create a new lumen in the patient's vessel. The burrincludes a nose and end section with an elastic tube section coupled inbetween. The burr is expanded due to centrifugal force. A portion of thetube section is coated with an abrasive such that the tube section willablate an occlusion as the burr is rotated and advanced through avessel.

In one embodiment, the expansion control mechanism includesreinforcement fibers embedded into the elastic tube section. Thereinforcement fibers prevent the tube section from over-expanding whenrotated. A portion of the tube section is coated with an abrasive suchthat the expanded tube section will ablate an occlusion as the burr isrotated and advanced through a vessel.

In another embodiment, the tube includes inner and outer layers with theexpansion control mechanism containing a layer of ePTFE disposedin-between the inner and outer cast film layers. The ePTFE layerprevents the ablation burr from over-expanding.

In another embodiment, the expansion control mechanism includes postcross-linking of the tube section. The post cross-links prevent theablation burr from over-expanding.

In yet another embodiment, the expansion control mechanism includescurvilinear ribs on the interior of the tube section. The curvilinearribs prevent the ablation burr from over-expanding.

In yet another embodiment, the expansion control mechanism includesalternating braided layers of a non-elastic polymeric materialin-between the inner and outer layers of the tube section. Thealternating braided layers prevents the ablation burr fromover-expanding.

According to another aspect of the present invention, a reversepull-back ablation burr system includes an ablation burr having anabrasive disposed on its proximal end for ablating an occlusion when theburr is pulled back through the occlusion toward the guide catheter. Thesystems further include an aspiration catheter that aspirates the loosegromous that is ablated by the ablation burr.

In one embodiment, the system prevents the loose gromous of a SaphenousVein Graft from reembolizing by using the ablation burr in its expandedstate as a seal. The burr is pulled back in a reverse fashion to ablatethe lesion. Similarly, a distal balloon or filter could be deployed toprevent accident embolization.

In another embodiment, the system prevents the loose gromous fromreembolizing by including a self expanding seal coupled to theaspiration catheter. The seal is deployed after the ablation burr isrouted through the lesion. As the burr is pulled back in a reversefashion to ablate the lesion, a vacuum is applied to the aspirationcatheter to remove the loose gromous from the vasculature.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIGS. 1A and 1B illustrate an expandable balloon ablation burr accordingto a first embodiment of the present invention;

FIGS. 2A-2D illustrate an ablation burr with an expandable end accordingto a second embodiment of the present invention;

FIGS. 3A-3D illustrate an expandable burr that is formed from a strip ofsuperelastic material according to a third embodiment of the presentinvention;

FIGS. 4A and 4B illustrate an expandable spring ablation burr includingan indexing mechanism to control the outer diameter of the burraccording to another aspect of the present invention;

FIG. 5A illustrates an isometric view of an ablation burr including anindexing mechanism for selectively changing the outer diameter of theburr according to another aspect of the present invention;

FIG. 5B illustrates the ablation burr shown in FIG. 5A with the partsshown in an exploded relationship;

FIGS. 6A and 6B illustrate another embodiment of an ablation burr withan indexing mechanism for selectively changing the outer diameter of theburr according to the present invention; and

FIGS. 7A and 7B illustrate yet another embodiment of an ablation burrwith an indexing mechanism for selectively changing the outer diameterof the burr according to the present invention.

FIG. 8 illustrates an expandable ablation burr including a expansioncontrol mechanism for the predetermining and controlling the maximumouter diameter of the burr according to another aspect of the presentinvention;

FIG. 9 illustrates a cross-sectional view of the expandable ablationburr of FIG. 8 having an expansion control mechanism for predeterminingand controlling the maximum outer diameter of the burr according toanother aspect of the present invention;

FIG. 10 illustrates a cross-sectional view of the expandable ablationburr of FIG. 9 having a expansion control mechanism for predeterminingand controlling the maximum outer diameter of the burr according toanother aspect of the present invention in its expanded state;

FIG. 11 illustrates a cross-sectional view of an expandable ablationburr of FIG. 9 having a expansion control mechanism for predeterminingand controlling the maximum outer diameter of the burr according toanother aspect of the present invention in its expanded state;

FIGS. 12A-12C illustrate an expandable ablation burr including aexpansion control mechanism to control the maximum outer diameter of theburr according to another aspect of the present invention;

FIGS. 13A-13B illustrate another embodiment of the expandable ablationburr including a expansion control mechanism to control the maximumouter diameter of the burr according to the present invention;

FIGS. 14A-14D illustrate yet another embodiment of the expandableablation burr including a expansion control mechanism to control themaximum outer diameter of the burr according to the present invention;

FIGS. 15A-15B illustrate still yet another embodiment of the expandableablation burr including a expansion control mechanism to control themaximum outer diameter of the burr according to the present invention;

FIGS. 16A-16C illustrate cross-sectional views of a reverse pull-backexpandable ablation burr system according to another aspect of thepresent invention;

FIG. 17A illustrates another embodiment of the reverse pull-backexpandable ablation burr system according to the present invention inits wrapped down state;

FIG. 17B illustrates the reverse pull-back expandable ablation burrsystem of FIG. 17A according to the present invention in its expandedstate;

FIG. 17C illustrates the reverse pull-back expandable ablation burrsystem of FIG. 17A according to the present invention in its expandedstate within an occluded vessel;

FIGS. 18A-18C illustrate cross-sectional views of the reverse pull-backexpandable ablation burr system of FIG. 17A according to the presentinvention;

FIG. 18D illustrates an expanded view of a cross-sectional view of theballoon in the reverse pull-back expandable ablation burr system of FIG.17A according to the present invention;

FIG. 19A illustrates a cross-sectional view of the reverse pull-backexpandable ablation burr system according to the present inventionbefore the burr has been routed through the lesion;

FIG. 19B illustrates a cross-sectional view of the reverse pull-backexpandable ablation burr system according to the present invention afterthe burr has been routed through the lesion;

FIG. 19C illustrates a cross-sectional view of the reverse pull-backexpandable ablation burr system according to the present invention afterFIG. 19B when the ablation burr is inflated;

FIG. 19D illustrates a cross-sectional view of the reverse pull-backexpandable ablation burr system according to the present invention afterFIG. 19C when the self-expanding seal is deployed;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As will be explained in further detail below, the present invention isan ablation burr having an outer diameter that may be expanded to exceedthe diameter of a guide catheter through which the burr is routed.Additionally, the present invention is an ablation burr including amechanism for selectively changing the outer diameter of the ablationburr so that varying sized lumens can be created in a patient's vesselusing the same burr. Further, the present invention is an ablation burrincluding a mechanism for controlling the ultimate or maximum outerdiameter of the ablation bur so as to prevent rupturing the burr ordamaging the vessel. Finally, the present invention is ablation systemincluding a reverse pull-back ablation burr and an aspiration sheath soas to prevent the ablated particulate from embolizing.

FIG. 1A illustrates an atherectomy device in accordance with a firstaspect of the present invention. The atherectomy device 20 is routedfrom a position outside a patient's body to a point near the site of avascular occlusion through a guide catheter 22. Extending through theguide catheter 22 is a drive shaft 24 that is coupled at its proximalend to a source of rotational motion such as an electric motor or gasturbine (not shown) that rotates the drive shaft 24 at high speed, e.g.,between 20,000 and 250,000 rpm. Disposed at a distal end of the driveshaft 24 is an ablation burr 28 that when rotated by the drive shaft 24ablates a new lumen through the occlusion in order to permit blood toflow freely through the vessel. Extending through the drive shaft 24 andthe ablation burr 28 is a guide wire 26 that can be steered by aphysician in order to guide the ablation burr through the vascularocclusion.

As indicated above, it is generally desirable that the ablation burr 28be routed through the smallest possible guide catheter to the point nearthe vascular occlusion. In the past, if the diameter of the vessel inwhich the occlusion was located was greater than the diameter of theablation burr, the entire atherectomy device including drive shaft,ablation burr and catheter had to be removed from the patient andreplaced with a larger diameter catheter that could accommodate a largerdiameter burr if all of the occlusion was to be removed. To facilitatemaximal lumen size after ablation, the maximum outer diameter of theablation burr 28 is expandable such that its maximum diameter exceedsthe diameter of the guide catheter used to route the burr to the site ofthe occlusion.

According to the embodiment of the invention as shown in FIGS. 1A and1B, the ablation burr 28 comprises a length of hypotube 30 coupled to adistal end of the drive shaft 24. The hypotube 30 includes one or moreholes 32 that allow fluid to flow in or out of the hypotube. Surroundingthe hypotube 30 is a polymeric balloon 34, having an abrasive 36disposed on at least a portion of the outer surface of the balloon. Thedistal end of the ablation burr 28 fits behind a concave surface of atip 37 that prevents the seal of the polymeric balloon from becomingunglued from the hypotube 30 as the burr is advanced through anocclusion.

When the drive shaft is not being rotated, the balloon 34 collapses intoan unexpanded state as shown in FIG. 1A. In its unexpanded state, theouter diameter of the ablation burr 28 is smaller than the innerdiameter of the guide catheter 22.

When the drive shaft 24 is rotated, fluid surrounding the drive shaft orwithin the drive shaft is expelled through the holes 32 in the hypotubeend into the balloon 34 causing the balloon 34 to expand to its maximumdiameter. The maximum diameter is generally larger than the innerdiameter of the guide catheter 22. The burr is then advanced through theocclusion to create a lumen in the patient's vessel. When the driveshaft 24 ceases to rotate, the balloon 34 collapses, and the burr can beremoved through the guide catheter 22.

In the presently preferred embodiment of the invention, the polymericballoon 34 is made from a non-stretchable plastic material such as anoriented polyethylene terephthalate polymer (PET). However, it isbelieved that other plastics or elastomeric materials may also be used.

The abrasive 36 disposed on the outer surface of the balloon preferablycomprises small diamond chips approximately 2-60 microns in size.

If the balloon 34 is made of PET, the abrasive 36 is secured to theballoon by creating a thin base layer of silver or gold using vacuumdeposition techniques. Once the base layer is applied to the balloon, alayer of metal such as nickel having a slurry of diamond particlesdisposed therein can be plated to the base layer using an electro- orelectroless plating method as is done with conventional burrs.

In some instances, it may be desirable to etch or mask a portion of thebase layer with a pattern of dots or other shapes so that the stiffnickel layer does not completely surround the balloon. If the abrasiveis only plated to the etched pattern, it may allow the balloon to moreeasily expand and collapse. In addition to electroplating, it isbelieved that other techniques could be used to secure the abrasive tothe balloon, such as by using an adhesive or chemically bonding sites onthe outer surface of the polymeric balloon to which metal ions such ascopper, silver, gold, or nickel may bond. These sites may be bonded tothe balloon surface using a high-vacuum plasma system or byincorporating chemicals (such as carbon, silver, etc.) with the polymerprior to the extrusion of the balloon. Alternatively, it is believedthat pulse cathode arc ion deposition could be used to incorporatebonding sites on the surface of the elastomer.

FIGS. 2A and 2B illustrate another embodiment of an expandable ablationburr according to the present invention. The expandable ablation burr 40is mounted to the distal end of a conventional drive shaft 24 thatrotates the burr at high speeds. A guide wire 26 extends through thedrive shaft 24 and the ablation burr 40 so that the burr can guidethrough a vascular occlusion. The burr is formed as a solid core (exceptfor the lumen through which the guide wire extends) that is made ofmetal or other suitable material and includes a generally bullet-shapednose section 42 having a maximum diameter that begins at approximatelythe midpoint of the burr and tapers in diameter to the distal tip of theburr. The burr 40 also contains a proximal stepped section 44 having asubstantially constant diameter that is less than the maximum diameterof the nose section.

Secured over the stepped section 44 of the burr with an adhesive or amechanical fastener is a polymeric tube 46 having an outer diameter thatis substantially equal to or greater than the maximum outer diameter ofthe nose section 42. The length of the polymeric tube 46 is preferablylonger than the length of the stepped section 44 such that a portion ofthe polymeric tube overhangs the proximal end of the solid core. Anabrasive coating is disposed on at least a portion of the outer surfaceof the tube 46 and the nose section 42. The abrasive is secured to thetube 46 in the same manner as the abrasive is secured to the expandableballoon described above.

When the drive shaft 24 is not rotated, the ablation burr 40 has amaximum outer diameter that is smaller than the inner diameter of aguide catheter 22 through which the burr is routed.

As shown in FIG. 2B, when the drive shaft 24 is rotated, the proximalend of the elastomeric tube 46 expands due to centrifugal force. Theproximal end of the ablation burr 40 extends radially outward, thereforeallowing the burr to ablate a larger lumen as it is advanced in avessel. As the drive shaft 24 is slowed, the centrifugal force on theproximal end of the polymeric tube 46 decreases and the outer diameterof the ablation burr returns to its unexpanded state. The ablation burrcan then be withdrawn from the patient through the guide catheter 22.

FIGS. 2C and 2D illustrate a cross-section of an alternative embodimentof the expandable ablation burr shown in FIGS. 2A and 2B. An ablationburr 40′ includes a generally solid core including a distal nose section42 and a proximal stepped section 44. A polymeric tube 46′ is bonded tothe stepped section 44 such that the outer diameter of the polymerictube is approximately equal to the maximum diameter of the nose section42 when the burr is in an unexpanded state. In contrast to theembodiment shown in FIGS. 2A and 2B, a proximal end 48 of the polymerictube 46′ is tapered to the drive shaft 24. In addition, the polymerictube 46′ may include one or more holes 50 disposed about its peripheryto control the outer diameter of the burr as the burr is rotated.

FIG. 2D illustrates the ablation burr 40′ as the drive shaft 24 isrotated. Centrifugal force causes a center section of the polymeric tubethat lies between the proximal end of the solid core and the proximalend 48 of the tube to expand radially outward. As the burr beginsspinning, centrifugal force expands the polymeric tube. Fluid then fillsthe interior cavity of the tube and is also acted on by the centrifugalforce. To prevent the tube from over expanding, fluid is allowed to ventout the one or more holes 50 that surround the tube 46′ such that thevolumetric rate at which the fluid vents from the tube reaches anequilibrium with the volumetric rate at which it enters the interior ofthe tube and the expansion of the tube is halted. The one or more holes50 increase in size as the speed of the burr increases and the tubeexpands. As the rotational speed of the ablation burr is decreased, theouter diameter of the burr decreases so that the burr can be withdrawnthrough the catheter. Because the end 48 of the polymeric tube 46′ isclosed to meet the drive shaft 24, the polymeric tube 46′ is less likelyto catch the distal end of the guide catheter as the burr is withdrawnfrom the patient.

Although the polymeric tube is preferably positioned at the proximal endof the burr, it may be advantageous to place the tube at the distal endof the burr in order to remove certain occlusions.

In simulated ablation tests, the ablation burrs illustrated in FIGS.2A-2D appear to cause less trauma to the vessel walls and a more evencutting than a conventional burr. In addition, the spinning polymerictube appears to self center the burr in the center of the patient'svessel. Finally, it is believed that the increased surface area of thepolymeric tube creates less heat at the point where it contacts theocclusion, thereby reducing the likelihood of vessel spasm damage orclotting.

It is currently believed that polymer used to make the polymeric tubeshould have a stress/strain characteristic that allows the materials tobe stretched to a known point but not beyond. One technique to achievethe desired stress/strain characteristics is to stretch the polymericmaterial as it cools. Alternatively, it is possible to incorporate aninelastic string or band into the tube that straightens as the tubeexpands and reaches a maximum size but cannot be stretched any further.

In some instances, it may be desirable to coat the outer surface of thecore and polymeric tube with a hydrophilic coating such as Hydropass™,available from Boston Scientific and described in U.S. Pat. No.5,702,754, which is incorporated herein by reference. The hydrophiliccoating attracts water molecules, thereby making the surface slipperyand easier to advance along the guide catheter. In addition, thehydrophilic coating may be beneficial during ablation since less torquemay be transferred to a vessel wall if the burr stalls. In addition, thedifferential cutting ability of the burr may be enhanced due to theincreased ability of the burr to slide over soft tissues.

FIGS. 3A-3D illustrate yet another embodiment of an expandable ablationburr according to the present invention. Secured to the distal end of adrive shaft 24 is a mandrel 60. The mandrel is cylindrical and has agenerally bullet-shaped nose at the distal and proximal ends and acentral lumen 62 extending through it so that the mandrel may bethreaded over a guide wire 26. A central portion 61 of the mandrel has areduced diameter compared to the maximum diameter of the distal andproximal ends. Surrounding the central cylindrical portion 61 of themandrel 60 is a metallic strip 64 that is coiled around the mandrel as aspring. The metallic strip 64 preferably has a length that is equal tothe length between the bullet-shaped ends of the mandrel 60 and a widththat is selected such that the strip wraps completely around the mandrelwith some overlap onto itself. The metallic strip 64 includes a tab 66that is fixed within a corresponding slot 68 disposed on the outersurface of the mandrel as shown in the cross-section FIG. 3B viewed fromthe distal end of the ablation burr. The tab is secured in the slot witheither an adhesive or by welding the tab in the slot.

At least a portion of the outer surface of the metallic strip 64 and thedistal end of the mandrel 60 is covered with an abrasive 72 that isplated onto the strip and mandrel in order to ablate a vascularocclusion when the ablation burr is rotated.

FIGS. 3C and 3D illustrate a cross section of the drive shaft, metallicstrip, and mandrel. In order to fit the ablation burr within the guidecatheter 22, the metallic strip 64 is more tightly wrapped around themandrel in order to reduce its outer diameter as shown in FIG. 3D. Uponemerging from the distal end of the catheter 22, the metallic strip willspring open to resume its original shape shown in FIG. 3C and its outerdiameter will therefore increase. Because the proximal and distal endsof the metallic strip 64 are tapered to follow the contour of thebullet-shaped ends of the mandrel, the metallic strip can berecompressed by pulling it into the distal end of the guide catheter 22.

In the presently preferred embodiment of the invention, the metallicstrip 64 is made of a superelastic metal such as Nitinol®.

As will be appreciated, to ablate an occlusion in a blood vessel, themetallic strip 64 must be rotated in the direction of the arrow 74 (FIG.3B) such that an edge 70 of the strip extending along the length of theburr trails the movement of the burr in order to avoid further uncoilingthe strip and possibly cutting into the vessel wall.

Yet another alternative embodiment of the expandable ablation burr ofthe present invention is shown in FIGS. 4A and 4B. The ablation burr 80includes a coiled wire spring 82 that is wound around the longitudinalaxis of a central drive tube 84. Plated to the outer surfaces of atleast some of the individual spring coils is an abrasive to ablate anocclusion in a patient's vessel as the burr is rotated. The spring 82 iswound into a generally ellipsoidal shape with a maximum diameter at amidpoint that is larger than the diameter of the guide catheter 22through which the burr is routed. The distal end of the spring 82 issecured to a nose cone 86 at the distal end of the burr while theproximal end of the spring is secured to the proximal end of the drivetube 84 by a band 85 that overlaps a few proximal coils of the spring.

The drive tube 84 has a proximal lumen 90 into which the distal end ofthe drive shaft 24 is inserted and secured. A distal lumen 92 of thetube receives a correspondingly shaped shaft 94 that extends from a rearsurface of the nose cone 86. The distal lumen 92 and the shaft 94 of thenose cone are shaped such that the shaft moves axially within the lumenbut cannot be rotated in the lumen. Therefore, any torque induced in thedrive tube 84 by the drive shaft 24 will be transmitted to the nose cone86 and the distal end of the spring 82. Although not shown in FIGS. 4Aand 4B, the drive tube 84 and nose cone 86 preferably include a lumenextending therethrough for passage of a guide wire.

When the ablation burr 80 is positioned in the guide catheter 22 asshown in FIG. 4A, the spring 82 is compressed, thereby reducing itsouter diameter. When the ablation burr 80 extends out the distal end ofthe guide catheter 22, as shown in FIG. 4B, the spring 82 expands intoits ellipsoidal shape, thereby increasing the maximum outer diameter ofthe burr. As the spring 82 expands radially outward, the shaft 94 of thenose cone 86 is drawn into the distal lumen 92. Rotation of the burrwill further draw the shaft 94 into the distal lumen 92 until theproximal end of the shaft engages the end of the lumen 92. The length ofthe lumen 92 and the shaft 94 of the nose cone therefore control themaximum diameter of the spring 82. As a burr is withdrawn into the guidecatheter 22, the spring 82 is compressed and the shaft 94 will movedistally in the lumen 92.

In many instances, it is desirable to have an ablation burr that canassume several fixed outer diameters. For example, when creating aninitial lumen in an occluded vessel, it is generally advisable toutilize the smallest diameter burr available. In the past, if the sizeof the lumen needed to be increased, the entire ablation burr had to beremoved from the patient and successively larger burrs used until alumen of the desired size was created. To eliminate the need formultiple ablation burrs, another aspect of the invention is an ablationburr with an indexable outer diameter. As the burr is rotated and passedover an occlusion, the outer diameter of the burr can be selectivelyincreased to remove additional occluding material from the vessel.

FIGS. 5A and 5B illustrate a first embodiment of an ablation burraccording to the present invention having an indexable outer diameter.The ablation burr 100 is disposed at the distal end of a drive shaft 24.The burr includes a central lumen so that the ablation burr can bepassed over a guide wire 104. Surrounding the drive shaft 24 is acatheter 106 having a flared distal end 108 that operates to aid inselectively changing the outer diameter of the burr in a mannerdescribed below.

To remove the occluding material from a vessel, the ablation burrincludes a number of leaf blades 110 that are secured between a nosecone 112 and a ring 113 at the distal end of the burr. The blades 110extend proximally over the burr to a leaf retaining ring 114 at theproximal end of the burr. At least a portion of each blade 110 iscovered with an abrasive 116 such that when the ablation burr 100 isrotated by the drive shaft 24, the abrasive 116 will remove occludingmaterial from a patient's blood vessel. A polymeric sleeve (not shown)preferably is positioned inside the blades 110 to prevent the bladesfrom causing excessive turbulence in the blood as the burr is rotated.

By selectively changing the distance between the proximal and distalends of the burr, the amount by which the blades may expand radiallyoutward changes, thereby allowing the burr to create varying sizedlumens in a vessel.

As shown in FIG. 5B, to control the diameter of the burr, the ablationburr 100 includes a tube 120 that transmits power from the drive shaft24 to the distal end of the burr. At the distal end of the tube 120 isan indexing ring 122 having a diameter that is larger than the diameterof the tube 120. In the proximal rim of the indexing ring 122 are anumber of slots 124. Each slot includes a first edge 126 that is cantedwith respect to the longitudinal axis of the tube 120 and a second edge128 that extends parallel to the longitudinal axis of the tube 120. Eachof the slots 124 disposed around the perimeter of the indexing ring hasa different depth that controls the outer diameter of the ablation burr.

Pinned to the proximal end of the tube 120 is a drive tube 130. Thedrive shaft 24 is secured to the proximal end of the drive tube 130. Inaddition, the drive tube 130 has a central bore through which the tube120 can fit. The drive tube 130 includes a longitudinally extending slot132 on its outer surface into which a pin 134 is fitted. The pin 134 issecured to the outer surface of the tube 120 so that the tube 120 canmove longitudinally within the drive tube 130 but torque from the drivetube 130 is transferred to the tube 120 or vice versa.

At the distal end of the drive tube 130 is a fixed washer 136. The fixedwasher 136 has a diameter that is larger than the diameter of the drivetube 130. The distal rim of the fixed washer 136 includes a number ofteeth 138.

Positioned over the indexing ring 122 is a slide washer 140. The slidewasher 140 has an inner diameter substantially equal to the outerdiameter of the indexing ring 122 and an outer diameter substantiallyequal to the outer diameter of the fixed washer 136. The proximal rim ofthe slide washer 140 contains a number of teeth 142 that mate with theteeth 138 of the fixed washer 136. The slide washer 140 also includes apin 144 that rides along the edges 126 and 128 of the slots 124 in theindexing ring 122. Finally, the burr includes a spring 150 disposedbetween the back surface of the ring 113 and the distal end of the slidewasher 140.

When rotated by the drive shaft 24 or due to the spring of the blades110, centrifugal force causes the blades 110 to be radially expanded,thereby compressing the tube 120 into the drive tube 130. This in turncauses the pin 144 to slide along a canted edge 126 of a slot 124 in theindexing ring 122. As the pin 144 travels along the canted edge 126, theteeth 142 on the slide washer 140 rotate with respect to the teeth 138on the fixed washer 136. This “cocks” the teeth of the fixed washer 136and the slide washer 140 just past their maximum points. The maximumdistance by which the drive tube 130 can be compressed over the tube 120is limited by the depth of the slots 124 extending around the index ring122, thereby limiting the diameter of the burr.

To index the ablation burr to its next outer diameter, the burr ispulled into the catheter 106. The flared distal end 108 of the catheterengages the blades 110 and compresses them and the spring 150 causes thepin 144 on the slide washer 140 to travel along the straight edge 128 ofa slot 124 to a position proximal to the slots of the indexing ring 122.The force of the spring 150 pushes the slide washer 140 proximallythereby causing the teeth 142 on the slide washer and the teeth 138 onthe fixed washer to seat and further rotate the pin 144 to the next slotaround the indexing ring 122.

In operation, a physician sets the diameter of the burr to the smallestsetting to ablate an initial lumen in the patient's vessel. Then, bysequentially spinning the burr, stopping it and retracting it into thecatheter, the diameter can be increased or decreased depending on theposition of the pin 144 over the indexing ring 122 until a desired lumendiameter is reached.

In the presently preferred embodiment of the invention, the variouscomponents of the indexable burr 100 are made by micro-machining.However, it is believed that other fabrication techniques such as metalinjection molding or insert molded plastic could also be used.

FIGS. 6A and 6B illustrate another embodiment of an indexable ablationburr according to the present invention. The ablation burr 200 includesa drive tube 204 into which the distal end of the drive shaft 24 isinserted and secured. The drive tube 204 also includes a race 206 thatcircumscribes the perimeter of the drive tube. The race 206 is cantedwith respect to the longitudinal axis of the drive tube such that therace traverses a portion of the length of the drive tube 204. Atraveling ball 208 rests within the race 206.

Disposed distal to the race 206 is a series of ratchet teeth 210 thatare cut into the outer surface of the drive tube 204. The teeth operateto discretely step the maximum outer diameter of the ablation burr andto transfer the rotational motion of the drive shaft 24 to the burr inconjunction with a rachet tab 216 as described below.

Disposed over the proximal end of the drive tube 204 is a proximallocking tube 212. The proximal locking tube 212 is generally cylindricalbut has a stepped section 214 at its distal end such that half theperimeter of the proximal locking tube 212 is removed. The locking tube212 also includes a ratchet tab 216 that extends inwardly from the innersurface of the locking tube in approximately the middle of the steppedsection 214. The ratchet tab 216 engages the ratchet teeth 210 when theproximal locking tube 212 is positioned over the drive tube 204.Finally, the proximal locking tube 212 includes a hole 218 that is cutin the outer surface of the locking tube 212 at a position proximal tothe stepped section 214. The hole 218 is sized such that a portion ofthe traveling ball 208 will extend through the hole 218 when theproximal locking tube 212 is positioned over the drive tube 204.

Axially aligned with the distal end of the drive tube 204 is a distallocking tube 220. The locking tube 220 is generally cylindrical but hasa stepped section 222 at its proximal end that mates with the steppedsection 214 of the proximal locking tube 212 when the proximal anddistal locking tubes are axially aligned. The stepped sections 214 and222 maintain a rotational coupling between the distal and proximal endsof the ablation burr while allowing the distance between the proximaland distal locking tubes to vary.

Surrounding the burr are a number of blades 226 that extend radiallyoutward from a ring 228. The ring 228 is held in place between a nosecone 230 and a locking ring 232 at the distal end of the burr. Thelocking ring is secured to the distal end of the distal locking tube220. The blades 226 are folded back over the outside of the burr and aresecured around the proximal end of the locking tube 212 by a leafretaining ring 236. Although not shown, the ablation burr 200 preferablyincludes a polymeric liner inside the blades 226 to prevent the bladesfrom causing excessive turbulence in the patient's blood as the burr isrotated.

Finally, the ablation burr 200 includes a traveling tube 240 that fitsover the proximal and distal locking tubes 212 and 220. The travelingtube 240 includes a hole 242 disposed in its perimeter. The hole forms adetent into which a top portion of the traveling ball 208 is seated. Thedistal rim of the traveling tube 240 engages the rear or the proximalsurface of the ring 228 from which the blades 226 extend.

To expand or contract the ablation burr 200, the drive shaft 24 isrotated in a direction that is opposite to the direction used duringablation while the blades 226 are held stationary. The ablation burr 200is retracted into a catheter having a distal end that captures theblades and holds them still as the drive shaft is rotated.

As shown in FIG. 6B, when the drive tube 204 is rotated in the clockwisedirection, the ratchet tab 216 rides over the ratchet teeth 210. Thiscauses the traveling ball 208 to move in the race 206 that extendsaround the outer surface of the drive tube 204 thereby pushing thetraveling tube 240 proximally or distally with respect to the drive tube204. Because the distal rim of the traveling tube 204 engages the rearor proximal surface of the ring 228 from which the blades 226 extend,the distance between the proximal and distal ends of the blades isvaried and hence the maximum expansion of the ablation burr iscontrolled.

When the drive tube 204 is rotated in the counterclockwise direction andthe blades 226 are free, the ratchet teeth 210 engage the ratchet tab216 causing the traveling tube to rotate with the burr and leaving thetraveling ball 208 in the same place in the race 206. Centrifigal forceon the blades 226 will cause the nose cone 230 to be drawn proximallyuntil the rear surface of the ring 228 engages the distal rim of thetraveling tube 240 and the expansion of the burr is halted. Therefore,by changing the position of the traveling tube 240 over the main tube204, the maximum diameter of the burr is controlled.

In operation, the physician may position the traveling ball in the racesuch that the burr has a minimum diameter in order to create an initiallumen in a vessel. Then the burr is then withdrawn into the catheter tohold the blades and the position of the traveling ball changed toincrease the size of the lumen without having to remove the atherectomydevice from the patient.

Again, parts of the ablation burr 200 are preferably made by machiningbut could be made by other techniques such as metal injection molding.

FIGS. 7A and 7B show another alternative embodiment of an indexableablation burr according to the present invention. The ablation burr 300includes a drive tube 302 into which the distal end of the drive shaft24 is inserted. The drive shaft 24 extends through drive tube 302 and issecured to a locking tube 320. The drive tube 302 is generallycylindrical except for a stepped semi-circular section 304 at the distalend of the tube, whereby half the circumference of the tube is removed.The drive tube 302 also includes a serpentine channel 306 disposed aboutthe outer surface of the tube proximal to the stepped section 304. Theserpentine channel 306 operates to control the maximum diameter of theablation burr in a manner described below.

Disposed over a proximal end of the drive tube 302 is a spring 310. Thespring abuts a ring 311 that is formed around the perimeter of the drivetube 302 to prevent the spring from moving forward on the drive tube.Also disposed over the proximal end of the drive tube 302 behind thespring 310 is a proximal locking tube 312. At its proximal rim, theproximal locking tube 312 includes a notch 314 into which a pin 316 thatextends radially outward from the proximal end of the drive tube 302 isinserted. The pin 316 operates to transfer rotation energy of the drivetube 302 to the proximal locking tube 312 while allowing the lockingtube 312 some axial motion along the drive tube.

Positioned distal to and axially aligned with the drive tube 302 is adistal locking tube 320. The distal locking tube 320 is generallycircular with a stepped semi-circular section 322 that mates with thestepped section 304 on the drive tube 302. At the distal end of the burrare a set of blades 330 that extend outwardly from a ring 332 and areheld in place at the distal end of the burr by a nose cone 334 and aretaining ring (not shown). The retaining ring is secured within thedistal end of the distal locking tube 320. The set of blades 330 aresecured at the proximal end of the burr to the outer surface of lockingtube 320. As with the indexable burrs described above, an elastomericliner is preferably positioned inside the blade to prevent excessiveturbulence of the blood in a lumen.

Extending over the drive tube 302 and the distal locking tube 320 is atraveling tube 340. At its proximal end, the traveling tube 340 includesa larger diameter flange 342 with a proximally extending tab 344 securedthereto. Extending radially inward from the end of the tab 344 is afollower pin 346.

As shown in FIG. 7B, the tab 344 and follower pin 346 operate as a camwithin the serpentine track 306 that is formed around the outer surfaceof the drive tube 302. The track 306 includes a number of alternatingbends 308, 310 that open towards the distal and proximal ends of thedrive tube 302, respectively. Each of the bends 308 that open towardsthe distal end of the drive tube 302 are located at a different positionalong the length of the drive tube 302.

The depth of the channel 306 varies as the channel proceeds around thedrive tube 302. Positioned in the channel near each of the bends 308,310 is a step 354. At each step, the depth of the channel increases. Thedepth then decreases in the channel until the next bend where the depthagain increases with a step. This pattern continues around thecircumference of the drive tube 302.

As the ablation burr 300 is pulled into a catheter having a distal endwhich prevents the collapse or bending of the blades 330, a pull on thedrive coil causes retraction of the drive tube 302. This causes arelative movement of the traveling tube 340 in a distal direction(relative to the drive tube). The follower pin 346 will move to a distalend of the slot in the serpentine channel 306. Releasing the drive coilwill allow spring 310 to move the drive tube 302 distal which willresult in the traveling tube pin moving into a proximal end of the slotin the serpentine channel 306. As the pin 346 moves back and forth inthe channel, it is forced to move in one direction due to a series oframps in the channel. As the pin 346 moves to the distal end of a slot,it moves over a ramp which prevents it from returning back down thatslot. It is forced to return at an angle down to the adjacent slot.Before reaching the bottom of the adjacent slot, it again travels over aramp, which prevents it from returning up the slot it had just traveleddown. The pin is now in an analogous position to the position in whichit started. Because the proximal end of each slot is at a slightlydifferent position (along a proximal/distal line on the drive tube), theoverall length of the burr is therefore adjusted with eachproximal/distal movement of the pin.

In many instances, it is desirable to have an expandable ablation burrthat can expand in a controlled manner to an ultimate or maximum outerdiameter. As discussed above, the present invention is an expandableatherectomy burr that can treat different size vessels while beingtraversed through a small guide catheter. However, it is important thatthe burr does not expand too far. For example, when using an elasticpolymeric material for the expansion tube of the burr, over-expansion ofthe burr may stretch the burr beyond the elastic range resulting in apermanent, non-recoverable deformation of the burr. To eliminate theneed for multiple ablation burrs, another aspect of the invention is anexpandable ablation burr with a controlled, ultimate or maximum outerdiameter. As the burr is rotated and passed over an occlusion, theablation burr expands to a maximum outer diameter. The expandableablation burr with a maximum outer diameter removes the occludingmaterial from the vessel, without the possibility of over-expansionresulting in a ruptured burr or dilated vessel.

FIGS. 8-12C illustrate various embodiments of an ablation burr accordingto the present invention having a controlled expansion with a maximumouter diameter. The atherectomy device 420 is routed from a positionoutside a patient's body to a point near the site of a vascularocclusion 410 through a guide catheter 422. Extending through the guidecatheter 422 is a drive shaft 424 that is coupled at its proximal end toa source of rotational motion such as an electric motor or gas turbine(not shown) that rotates the drive shaft 424 at high speed, e.g.,between 20,000 and 250,000 rpm. Disposed at a distal end of the driveshaft 424 is an ablation burr 428 that when rotated by the drive shaft424 ablates a new lumen through the occlusion in order to permit bloodto flow more freely through the vessel. Extending through the driveshaft 424 and the ablation burr 428 is a guide wire 426 that can besteered by a physician in order to guide the ablation burr through thevascular occlusion 410.

As best shown in FIGS. 9-11, the expandable ablation burr 428 comprisesa bullet-shaped nose section 430 coupled to the distal end of driveshaft 424 and a similarly shaped proximal end section 432 in slidingengagement over drive shaft 424. A central lumen 434 extends through endsection 432 and a portion of nose section 430 to accommodate drive shaft424. Nose section 430 is preferably made from a metal material such asbrass or the like and is bonded to the drive shaft 424 by an adhesivesuch as epoxy or the like. Nose section 430 has a maximum diameter thatbegins proximally and tapers in diameter to the distal tip of the burr.Nose section 430 further contains a proximal stepped portion 444 havinga diameter that is less than the maximum diameter of the nose section430. Located at the distal end of nose section 430 and having a smallerdiameter than central lumen 434 is guide wire lumen 438. Guide wirelumen 438 extends through the tip of nose section 430 so that theablation burr may be threaded over guide wire 426.

The proximal end section 432 of ablation burr 428 is preferably madefrom a polymeric material such as polyurethane or the like and has amaximum diameter that begins distally and tapers in diameter to theproximal tip of the burr. The end section 432 further contains a distalstepped portion 446 having a diameter that is less than the maximumdiameter of the end section 432. The proximal end section 432 may bondedto the drive shaft 424 so that end section 432 rotates with the driveshaft to prevent the tube section from twisting. In an embodiment thatdoes not bond the end section 432 to the drive shaft 424, the innersurface of end section 432 includes a rotational lock, which isdescribed in detail below, so that the end section can slide axiallyalong the drive shaft 424 but cannot rotate separately from drive shaft424. Therefore, any torque induced by the drive shaft 424 will betransmitted to end section 432.

The rotational lock is comprised of a square shaped bore that extendsthrough end section 432 and a drive shaft with a corresponding shapemateable with end section 432 so that the rotational motion of the driveshaft is transferred to the end section 432. A square shaped metal tubecould be bonded to the drive shaft 424 or the drive shaft 424 could becrimped or ground to a square to provide the corresponding shape torotate end section 432. It should be appreciated to one of ordinaryskill that other structures may be used to provide the features of therotational lock such as a pin/slot arrangement.

Attached to the corresponding stepped portions 444, 446 of nose and endsections is tube or sheath section 440, having an abrasive 436 disposedon at least a portion of the outer surface of the tube section. Tubesection 440 is made from a stretchable polymeric or elastomericmaterial. It is desirable for the material to have a hardness in therange of 50 to 80 shore A and a tensile modulus at 50% elongation ofapproximately 300 psi in order to expand. Such a material with theseproperties is a polyurethane made by Dow and sold under the namePellethane 2103, 70A. However, it is believed that other plastics orelastomeric materials with these properties may also be used.

As shown in FIGS. 12A-12C, reinforcement fibers 442 are embedded intotube section 440 to improve strength, control burr shape duringexpansion, and determine the ultimate or maximum tube section expansiondiameter. The reinforcement fibers 442 are preferably made ofpolyethylene such as Spectra 1000, 50D, produced by AlliedSignal.However, other fibers such as hydrophilic treated nylon or liquidcrystal fiber may be used.

The fiber reinforced polymeric tube section 440 is made by firstextruding a small diameter tube of polymeric material. The reinforcementfibers are then braided on the outside surface of the small diametertube by a conventional braiding machine. A second, larger diameter tubeof polymeric material is then extruded over the braided small diametertube. The heat and pressure from the final extrusion creates the unitarytube section 440.

The abrasive 436 disposed on the outer surface of the tube sectionpreferably comprises small diamond chips approximately 2-60 microns insize. Abrasive 436 is secured to the tube using an electro and/orelectro-less plating method. This method has been previously describedin conjunction with the embodiment of the present invention shown inFIG. 1. Other methods such as high-vacuum or pulse cathode arc iondeposition may also be used as earlier described.

FIG. 10 illustrates the ablation burr 428 as the drive shaft 24 is beingrotated. Centrifugal force causes the center section of the tube section440, that lies between the proximal end of nose section 430 and thedistal end of end section 432, to expand radially outward. As the burrbegins spinning, centrifugal force initiates expansion of tube section440. Fluid then fills the interior cavity of the tube section throughdrive shaft 424, which is also acted on by the centrifugal force. As therotational speed of the ablation burr continues to increase, the shapeof tube section 440 is controlled at least in part by reinforcementfiber 442. The tube reaches its predetermined maximum outer diameter ata set rotational speed. Even if the burr is rotated past this setrotational speed, the tube section is prevented from further expandingdue to reinforcement fibers 442 which are embedded in the tube. As therotational speed of the ablation burr is decreased, the outer diameterof the burr decreases so that the burr can be withdrawn through theguide catheter that surrounds the driveshaft.

It will be appreciated to one of ordinary skill in the art that thedimensions and patterns of the fiber reinforcement is determined by themechanical requirements of the composite burr and can be used todetermine the maximum expansion diameter of the burr so as to avoidrupturing the burr or dilating the vessel. For example, the braid piccount, or the number of cross points of the fiber per inch of length,may vary to allow the tube section to expand to a certain predeterminedamount. A pic count in the range of 10-30 has been used with Pellethane2103 70A to allow for ample expansion but also still possessing theability to restrict the expansion of the tube to a definite maximumouter diameter. However, different pic count ranges may be used withdifferent polymeric materials.

FIGS. 13A-13B illustrate another embodiment of a maximum outer diameterablation burr according to the present invention. As shown in FIG. 13A,the expandable ablation burr 450 is mounted to the distal end of aconventional drive shaft (not shown) that rotates the burr at highspeeds. Ablation burr 450 includes a tube or sheath section 460 withproximal and distal ends and having an abrasive 468 disposed on at leasta portion of the outer surface of the tube. The distal end of tubesection 460 is attached to the reduced diameter stepped portion 456 ofthe nose section 452 and the proximal end of the tube is attached to thereduced diameter stepped portion 458 of end section 454 in a mannersimilar to as previously describe in FIG. 9 for ablation burr 428. Tubesection 460 contains two layers 462, 464 of a stretchable cast film. Anintermediate layer 466 of expanded polytetrafluoroethylene (referredhereinafter as ePTFE) with a pore size of about 1 micron is disposedbetween the layers of cast film to control the shape and expansion ofthe burr. This is achieved because ePTFE has a natural characteristic ofgrowing narrower as it is stretched. By holding the width constantbetween the cast film layers, the ePTFE will have a limited ability tostretch.

The tube section 460 is made by first applying a 5% solution oftetrahydrofuran (THF) and polyurethane to the top and bottom surfaces ofthe ePTFE layer 466 and allowing the solution to penetrate. Cast filmlayers 462, 464 are placed on both sides of the ePTFE and wrapped arounda mandrel. The wrapped tube is heat set at about 160 degrees Celsius forapproximately 30 minutes to fuse the layers together to form unitarytube section 460.

In operation, as previously described in FIG. 9, the ablation burr 450is rotated by a drive shaft (not shown). Centrifugal force causes acenter section of the polymeric tube section 460, that lies between theproximal end of nose section 452 and the distal end of end section 454,to expand radially outward. As the burr begins spinning, centrifugalforce initiates expansion of tube section 460. Fluid then fills theinterior cavity of the tube through drive shaft 424 and is also acted onby the centrifugal force. As the rotational speed of the ablation burrcontinues to increase, the shape of tube section is controlled by ePTFElayer 466. The tube reaches its predetermined maximum outer diameter ata set rotational speed. Even if the burr is rotated past this setrotational speed, the tube section is prevented from over expanding dueto ePTFE layer 466 which is fused between cast film layers 462, 464 oftube section 460. As the rotational speed of the ablation burr isdecreased, the outer diameter of the burr decreases so that the burr canbe withdrawn through the catheter.

The abrasive 468 is disposed at the distal end of the outer surface ofthe tube section 460, and preferably comprises small diamond chipsapproximately 2-60 microns in size. Abrasive 468 is secured to the tubeusing an electro or electro-less plating method. This method has beenpreviously described in the embodiment shown in FIG. 1. Other methodssuch as high-vacuum or pulse cathode arc ion deposition may also be usedas earlier described.

In the above-described embodiment, the use of one layer of ePTFE wasdescribed. However, it may be desirable to use multiple layers disposedat different angles with respect to each other to control the expansionof the burr. Further, in the above-described preferred presentembodiment, the cast film is a polymeric material such as polyurethane.However, other polymeric or elastomeric material may be used.

In another embodiment of the invention, a stretchable material withpost-crosslinking capabilities is extruded into a tube or sheathsection. The tube section (not shown) having an abrasive disposed on atleast a portion of the outer surface of the tube section, is used as theexpandable section of the ablation burr. The tube section is crosslinkedby exposing the tube to radiation. The tube section may also becrosslinked by a water initiated crosslinking function group during theextrusion quench process. The expansion of the tube can be controlled oradjusted by the crosslinking density.

Abrasive is disposed at the distal end of the outer surface of the tubesection, and preferably comprises small diamond chips approximately 2-60microns in size. The abrasive is secured to the tube section using anelectro or electro-less plating method. This method has been previouslydescribed in the embodiment shown in FIG. 1. Other methods such ashigh-vacuum or pulse cathode arc ion deposition may also be used asearlier described. Further, in the preferred present embodiment, thepost-crosslinking tube may be a polymeric material such as polyurethane.However, other polymeric or elastomeric material with post-crosslinkingcapabilities may be used.

FIGS. 14A-D illustrate another embodiment of a maximum outer diameterablation burr according to the present invention. As shown, anexpandable ablation burr 470 is mounted to the distal end of aconventional drive shaft (not shown) that rotates the burr at highspeeds. The ablation burr 470 includes a stretchable tube or sheathsection 480 with proximal and distal ends. The distal end of the tubesection 480 is attached to a reduced diameter the stepped portion 476 ofthe nose section 472, and the proximal end of the tube section isattached to a reduced diameter stepped portion 478 of end section 474 aspreviously described with respect to FIG. 9.

As shown in FIGS. 14A and 14C, tube section 480 in an unexpanded stateincludes curvilinear ribs 482 extending longitudinally from nose section472. Curvilinear ribs 482 are nominally spiraled along the length of theburr 470. As shown in FIG. 14C, curvilinear ribs 482 are formed asrelatively thick internal ridges extending radially inward from theouter surface of tube section 480. Curvilinear ribs 482 alternatebetween channel-like sections 484 on the inner surface of the tubesection. Channel-like sections 484 also extend radially inward. However,as compared to curvilinear ribs 482, channel-like sections 484 do notextend inward as far so as to create a tube section having a wall withalternating thickness.

The abrasive 486 is disposed on the outer surface of the tube sectiondirectly above internal ribs 482, and preferably comprises small diamondchips approximately 2-60 microns in size. By disposing the abrasivedirectly over the internal ribs on the outer surface of the tubesection, the shear force between the abrasive 486 and the tube section480 is reduced when section 480 expands (shown in FIG. 14B), allowingthe abrasive to adhere to the tube section better than a uniformelastomer Abrasive 486 is secured to the tube using an electro orelectro-less plating method as described above. Other methods, such ashigh-vacuum or pulse cathode arc ion deposition, may also be used asearlier described.

FIG. 14B illustrates the ablation burr 470 as the drive shaft 424 isrotated. Centrifugal force causes the tube section 480 that lies betweenthe proximal end of nose section 472 and the distal end of end section474, to expand radially outward. As the burr begins spinning,centrifugal force expands the tube section. Fluid then fills theinterior cavity of the tube section 480 through drive shaft 424 and isalso acted on by the centrifugal force. To prevent the tube section 480from over expanding, the tube section expands only at the channel-likesections 484 located between the ribs. As the channel-like sections 484stretch and the tube section expands, the curvilinear ribs 482 begin tostraighten. Once the ribs straighten, further expansion of the tubesection 480 is inhibited. As the rotational speed of the ablation burris decreased, the outer diameter of the burr decreases so that the burrcan be withdrawn through the catheter.

In the preferred present embodiment, the expanding tube or sheathsection 480 is made from a polymeric material such as polyurethane.However, other polymeric or elastomeric material may be used.

It will be appreciated to one of ordinary skill in the art that thedimensions of the curvilinear ribs can be chosen to determine themaximum expansion diameter of the burr so as to avoid rupturing theburr.

FIGS. 15A-15B illustrate another embodiment of an ablation burraccording to the present invention. Referring to FIGS. 15A-15B, theexpandable ablation burr 490 is mounted to the distal end of aconventional drive shaft 424 that rotates the burr at high speeds.Ablation burr 490 includes a tube section 500 with proximal and distalends having an abrasive 510 disposed on at least a portion of theoutside surface of the tube. The distal end of tube section 500 isattached to the stepped portion 496 of the nose section 492 and theproximal end of the tube is attached to the stepped portion 498 of endsection 494 as previously described in connection with the embodimentshown in FIG. 9. As shown in FIG. 15A, tube section 500 includes twotubes 502, 504 of a polymeric material such as polyurethane orpolyethylene. Braided layers of fiber 506, 508 are located in-betweenpolymeric tubes 502, 504 to control the expansion of the burr.

Still referring to FIG. 15A, a polymeric material is extruded into smalldiameter tube 502. The inner tube 502 is placed onto a braiding machine(not shown) and a layer of fiber 506 is wrapped around the tube at anangle α. A second layer of fiber 508 is wrapped around the first layerof fiber 506 at an angle θ. Angle θ is usually the same angle as angle αof the first layer but in the opposite direction. The fibers of thesecond layer is oriented at an angle θ to with respect to the fibers ofthe first layer. A final outer tube 504 of polymeric material isextruded over the layered fibers to create a unified tube section 500.The abrasive 510 is disposed at the distal end of the outer surface ofthe tube section 500 and preferably comprises small diamond chipsapproximately 2-60 microns in size. Abrasive 510 is secured to the tubeusing an electro or electro-less plating method as described above.Other methods such as high-vacuum or pulse cathode arc ion depositionmay also be used as earlier described.

As the drive shaft is rotated, the ablation burr is expanded due tocentrifugal force. Prior to expansion, the layers of fibers are disposedwith respect to each other at a predetermined angle β. As the tubesection expands, the fiber layers follow the expansion of the tubesection by moving toward a position that is transverse to thelongitudinal axis of the burr. This movement causes angle θ and angle αto change. As soon as the angle β reaches 47.2 degrees, or the neutralangle, the fiber layers stop moving or expanding with the tube section.The stoppage in the movement of the fiber layer restricts the outerdiameter of the burr from expanding past this maximum diameter. A moredetailed explanation of this can be found in U.S. Pat. No. 4,706,670,which is incorporated herein by reference. As the rotational speed ofthe ablation burr is decreased, the outer diameter of the burr decreasesso that the burr can be withdrawn through the catheter.

It will be appreciated to one of ordinary skill in the art that multiplelayers of fiber may be wound around the small diameter tube. It willalso be appreciated that the fibers can be arranged at anypre-determined angle β so that the desired ultimate expansion diametercan be achieved.

In the presently preferred embodiment of the invention, the fibersshould be relatively non-elastic, but flexible and should have asuitable denier size in order to make a thin wall composite structure.An example of such a fiber is a liquid polymer crystal sold under thename Vectran®. However, other fibers having these characteristics mayalso be used.

With respect to the above discussed embodiments and any other potentialembodiments, it may be desirable to etch or mask a portion of the tubeso that the abrasive plating is laid in a pattern of dots or othershapes so that the abrasive layer does not completely surround the tube.If the abrasive is only plated to the etched pattern, it may allow thetube to more easily expand and collapse.

As can be seen from the above description, the present inventionprovides various mechanisms for controlling the maximum expandeddiameter of an ablation burr. By controlling the expanded diameter ofthe burr, it is not necessary to remove the burr, drive shaft andcatheter in order to ablate a larger diameter lumen in a patient.

In many instances, it is desirable to have an expandable ablation systemthat prevents the loose ablated particulate or gromous from embolizinginto a distal vasculature. In Saphenous Vein Grafts (SVG) and In-stentRestenosis, the occluded material or gromous is friable, andconventional devices may break off large pieces of this material rathereasily. This can cause the loose material or ablated particulate to flowdownstream and embolize. To eliminate the need for multiple ablationburrs and to aid in the prevention of ablated particulate flowingdownstream and embolizing, another aspect of the invention is a reversepull-back ablation burr system that ablates the occlusion in a patient'svessel. The reverse pull-back ablation burr removes the occludingmaterial from the vessel while reducing the possibility of the ablatedparticulate from embolizing.

FIGS. 16A-16C illustrate an embodiment of an ablation burr systemaccording to the present invention that uses a reverse pull-back burr toablate an occlusion. The atherectomy device 520 is routed from aposition outside a patient's body to a point near the site of a SVGlesion through a guide catheter 522. Extending through the guidecatheter 522 is an aspiration catheter or sheath 528 and a drive shaftthat is coupled at its proximal end to a source of rotational motionsuch as an electric motor or gas turbine (not shown) that rotates thedrive shaft 524 at high speeds, e.g., between 20,000 and 250,000 rpm.Disposed at the distal end of the drive shaft 524 is an ablation burr530 that when rotated by the drive shaft 524 ablates a new lumen throughthe occlusion in order to permit blood to flow freely through the vessel518. Extending through the drive shaft 524 and the ablation burr 530 isa guide wire 526 that can be steered by a physician in order to guidethe ablation burr through the SVG occlusion.

Referring to the embodiment of the present invention as shown in FIGS.16A-16C, the ablation burr 530 comprises a length of hypotube 532coupled to a distal end of the drive shaft 524. The hypotube 532includes one or more holes 534 that allow fluid to flow in or out of thehypotube 532. Surrounding the hypotube 532 is a polymeric balloonsection 536 with proximal and distal ends, having an abrasive 538disposed on at least a portion of the outer surface of the balloon.Referring to FIG. 16B, polymeric balloon section 536 is bonded at itsproximate and distal ends to the hypotube 532.

As shown in FIGS. 16A-C, a smooth surface 540 of balloon section 536begins at approximately the midpoint of balloon section 536 and extendsto its distal end. Smooth side 540 helps to prevent the ablation burr530 from scraping the vessel wall that may cause irritation and weakenthe vessel. Abrasive 538 is attached to the proximal half end of balloonsection 536 to remove the occluded material or gromous 542 when theablation burr 530 is pulled back toward the guide catheter 522.

Balloon section 536 in an unexpended state (not shown) is furled orfolded around the hypotube 532 so that ablation burr 530 has a minimaldiameter that may be positioned through the occluded vessel. Balloonsection 536 may be furled like convention percutaneous transluminalcoronary angioplasty (PTCA) balloons as shown and described in U.S. Pat.No. 5,342,307, which is incorporated herein by reference. When theablation burr 530 is in its furled condition and routed through theocclusion, abrasive 538 is partially covered by the smooth side 540 ofthe balloon section to prevent the breaking off of gromous 542.Alternatively, a sheathed balloon (not shown) or thin tube may be placedover the ballon section 536 to ease in the placement of the burr. Thesheathed balloon covers the abrasive when routed to the distal end ofthe occlusion, and then may be pulled off when the burr is ready toexpand.

Referring again to FIG. 16A, balloon section 536 in an expanded statewill have a maximum outer diameter which is small enough not to dilatethe SVG, but large enough to create a seal 544 and prevent ablatedparticulate from flowing past the ablation burr. The seal may have aboundary layer of fluid at the smooth side 540 of the balloon section536 or may be coated with a hydrophilic coating such as Hydropass™.Alternatively, a distal ballon (not shown) or filter (not shown) couldbe deployed at the distal side of the burr so as to prevent ablatedparticulate from embolizing.

In operation, ablation burr 530 is routed through the SVG lesion onguide wire 526 in its furled state. Once past the lesion, ablation burr530 is spun up to speed by drive shaft 524, which is rotated byrotational means such as a gas turbine or an electric motor. When thedrive shaft 524 is rotated, fluid surrounding the drive shaft or withinthe drive shaft enters balloon section 536 through holes 534 in hypotube532 to force the balloon to unfurl and expand to its maximum diameter toseal the vessel. Once the burr is rotated to its maximum speed and aseal 544 is created by the balloon section 536, the burr is pulled backthrough the lesion toward the guide catheter 522. As the burr passesthrough the lesion, abrasive 538 ablates the occluded material orgromous 542 and ablated particulate 546 is detached from the vesselwall. The seal 544 created by the balloon section 536 prevents thisablated particulate 546 from flowing downstream and possibly embolizing.Aspiration catheter 522 develops a slight vacuum with respect to bloodpressure in the range of negative 25 to positive 120 mm of mercury toaspirate the ablated particulate 546 from the vessel 518. After the newlumen in formed in the vessel 518, the rotation of ablation burr 530 isreduced so that the burr may be withdrawn through guide catheter 522.

The balloon section 536 refurls back into its original, unexpanded stateas soon as the ablation burr 530 ceases to rotate and the inflationfluid withdraws from the inner cavity of balloon section. The ability torefurl back into its original shape like conventional PTCA balloons isnot the subject of the present invention. A more detailed description ofa conventional PTCA balloon that can refurl back to its original shapeis shown and described in U.S. Pat. No. 5,456,666, which is incorporatedherein by reference.

In the presently preferred embodiment of the invention, balloon section536 is made from a non-stretchable or non-compliant plastic materialsuch as an oriented polyethylene terephthalate polymer (PET) or Mylar.However, other non-compliant polymeric or semi co-polymeric material maybe used.

The abrasive 438 disposed at the proximal end of the outer surface ofthe balloon preferably comprises small diamond chips approximately 2-60microns in size. Abrasive 438 is secured to the tube using an electro orelectro-less plating method. This method has been previously describedin the embodiment shown in FIG. 1. Other methods such as high-vacuum orpulse cathode arc ion deposition may also be used as earlier described.The abrasive may be plated in a triangular pattern on the proximal endbetween the folds of the balloon.

Alternatively, as shown in FIG. 16C, hypotube 532 may be constructed intwo sections. Balloon section 536 is bonded to a distal hypotube section548 and a proximal hypotube section 550. In this configuration, holes534 are not required in the hypotube sections to allow fluid to enterthe interior space of balloon section 536. Fluid enters through driveshaft 524, hypotube sections 548, 550 to expand balloon section 536.

FIGS. 17A-19C illustrate another embodiment of an ablation burr systemaccording to the present invention that uses a reverse pull-back burr toablate the occlusion. The ablation device is routed from a positionoutside a patient's body to a point near the site of a SVG lesionthrough a guide catheter (not shown). Extending through the guidecatheter is an aspiration catheter or sheath 574 and a drive shaft 576(FIGS. 19A, 19B) that is coupled at its proximal end to a source ofrotational motion such as an electric motor or gas turbine (not shown)that rotates the drive shaft 576 at high speeds, e.g., between 20,000and 250,000 rpm. Disposed at the distal end of the drive shaft 576 is anablation burr 580 that when rotated by the drive shaft 576 ablates a newlumen through the lesion 566 in order to permit blood to flow freelythrough the vessel 568. Extending through the drive shaft 576 and theablation burr 580 is a guide wire 578 that can be steered by a physicianin order to guide the ablation burr through the SVG lesion.

Referring to FIGS. 18A-18C, the ablation burr 580 includes a torquableinner tube 582 coupled to a distal end of the drive shaft 576. The innertube 582 includes one or more holes 584 that allow fluid to flow into orout of the inner tube 582. Surrounding the inner tube 582 is a balloonsection 586 with proximal and distal ends 588, 590. A wire mesh 592 isdisposed over the proximal end 588 of the balloon section and has anabrasive (not shown) disposed on at least a portion of its outersurface. Referring to FIGS. 18B and 18C, balloon section 586 is bondedat its proximal and distal ends to the inner tube 582.

The inner tube 582 includes an inflation lumen 596 that is coupled to aperfusion pump (not shown) that supplies saline or other fluid needed toinflate the balloon. The inflation lumen 596 extends through the innertube 582 to accommodate guide wire 578. A distal seal 598 is disposedaround the guide wire 578 at the distal end of inner tube 582 to createa closed, sealed inner tube so the perfusion system may operate toexpand the balloon. The distal seal 598 is a conventional seal such asan o-ring or the like.

As shown in FIG. 18A, the proximal end 588 of balloon section 586 isbonded to the outer surface of the proximal end of inner tube 582. Driveshaft 576 surrounds and is coupled to the proximal end 588 of theballoon. An outer tube 600 is secured to the drive shaft 576 by welding,brazing or the like. Outer tube 600 is disposed around the drive shaft576 and is concentric to inner tube 582. Outer tube 600 is preferablymade out of PTFE to provide a lubricious surface when routing theablation burr through the vasculature.

As shown in FIG. 17B, wire mesh 592 is coupled to the balloon 586 sothat the proximal end 588 of the balloon forms a concave shaped section602 when expanded. Wire mesh 592 begins at the proximal end 588 of theballoon and extends to approximately between the midpoint and the end ofthe balloon. In an actual embodiment, the wire mesh 592 extends from theproximal end of the balloon past the midpoint to approximately threequarters (¾) of the length of the balloon. The ends of wire meshterminate with a loop 604 of additional or stored wire (FIG. 18A). Theloop 604 allows for the wire mesh 592 to expand with the balloon whilecontrolling the balloon's shaped. Wire mesh 592 is embedded into theballoon 586 so that the outer surface of the mesh is approximately flushwith the outer surface of the balloon. Abrasive (not shown) is attachedto the exposed wire mesh to remove the occluded material 566 when theablation burr 580 is pulled back toward the guide catheter.

Also included in the ablation burr system is an aspiration catheter orsheath 574. Aspiration sheath 574 is routed through a guide catheter andcoupled to an aspiration pump/filter system (not shown) at its proximalend. The aspiration pump creates a slight vacuum in the range of minus10 mm of mercury to reverse the flow of the fluid and loose particulate606 so that it may be removed from the vessel 566. Coupled to the insidesurface of the aspiration sheath 574 is a self-expanding seal 608.

As seen in FIGS. 19C and 19D, the self expanding seal 608 includes apolymeric balloon 610 with a spring metal mesh 612 disposed within theballoon 610. Seal 608 has a maximum diameter slightly less than thevessel so that it blocks the blood flow through the vessel. Seal 608 iswithdrawn or pulled into aspiration sheath 574 by a wire (not shown) andassumes a compressible state. Referring to FIGS. 19A and 19B, selfexpanding seal 608 is deployed by advancing the seal out through thedistal end 575 of the aspiration catheter 574. Seal 608 self expands orsprings out to resume its original maximum diameter due to thecompression of the spring metal within the seal. In the presentlypreferred embodiment of the invention, the spring metal mesh 612 is madeof a superelastic metal such as Nitinol™.

Alternatively, a guide catheter (not shown) may serve as both the guidecatheter and the aspiration catheter. In this configuration, the selfexpanding seal would be coupled to and the aspiration pump/filter wouldbe in fluid flow communication with the dual purpose guide catheter.

As shown in FIG. 17A, the ablation burr 580 is routed through the guidecatheter and past the lesion in an unexpanded or wrapped down state. Inthe unexpanded state, the loops 604 of wire mesh 592 forms a forwardcutting surface on the outside surface of the balloon at approximatelythe distal quarter (front ¼) of the burr. If the lumen is too occludedto route the burr past the lesion, the burr is rotated and the forwardcutting surface ablates a passage through the lesion. The burr isrotated at a slower speed as compared to the rotational speed of theburr at its expanded state so as not to expand the burr.

In operation, as shown in FIG. 19A-19D, ablation burr 580 is routedthrough the lesion on guide wire 578 in its unexpanded or wrapped downstate. If the lumen in the vessel 568 is not large enough because of thelesion 566, the ablation burr 580 is rotated at a lower speed tomaintain a small diameter (i.e. 1.00-1.25 mm) to ablate a path as itpasses through the lesion to the distal end. Because wire mesh 592 formsa forward cutting surface when the burr is in an unexpanded state, alarge enough lumen is ablated to allow the burr to be routed past thelesion (FIG. 19B). Once past the lesion, the ablation burr 580 is spunup to speed by drive shaft 576 and perfusion is started by supplyingsaline to the inner tube 582. As the drive shaft 576 is rotated, fluidwithin the drive shaft enters balloon section 586 through holes 584 ininner tube 582 to force the balloon to expand. After perfusion hasbegun, the self expanding seal 608 is advanced and deployed at theproximal side of the lesion 566 as demonstrated in FIG. 19D. Once theseal is in place, the pressure at the ablation burr (distal pressure) isgreater than the pressure behind the seal (proximal pressure). A minus10 mm of mercury vacuum is created by the aspiration pump (not shown)and supplied to the aspiration sheath 574. The burr is expanded to alarger, first diameter (i.e. 2.00 mm) and pulled back toward theproximal side of the lesion. As the burr passes through the lesion,abrasive 594 ablates the occluded material and ablated particulate 606is detached from the vessel wall. The detached, ablated particulate 606is drawn into the aspiration catheter and removed from the vessel. Theburr is again advanced forward through the lesion to the distal side andexpanded to a larger, final diameter (i.e. 3.00 mm) for another passback through the lesion 566. The burr is rotated at a lower speed(20,000 rpm) to cause a more aggressive cut. The aggressive cuts resultin large ablated particulate 606 that must be removed through theaspiration sheath 574. A final pull back diameter is determined so thereis complete removal of the lesion. The final pull back diameter isdetermined by expanding the burr at the distal side of the lesion untilthe perfusion pressure in the vasculature rises suddenly. Ultrasound mayalso be used for the final pull back diameter of the burr. The finalpull back of the ablation burr 580 is performed slowly with carefulmonitoring of the distal pressure. After the new lumen in formed in thevessel 568, the rotation of ablation burr 580 decreases and theinflation fluid is withdrawn by the perfusion pump (not shown) so thatthe burr may be withdrawn through the guide catheter.

It will be appreciated by one of ordinary skill in the art that the burrwas described in operation as making two passes through the occlusion atparticular diameters. However, it may be desirable to make more or fewerpasses through the lesion at different diameters as needed to completelyremove the occluded material.

The abrasive (not shown) disposed at the proximal end 588 of the outersurface of the balloon preferably comprises small diamond chipsapproximately 2-60 microns in size. The abrasive is secured to the tubeusing an electro or electro-less plating method as described above.Other methods such as high-vacuum or pulse cathode arc ion depositionmay also be used as earlier described.

In the presently preferred embodiment, the balloon 586 is made of apolymeric material such as a polyolefin copolymer. However, otherpolymeric materials may be used. Further, it may be desirable to use aporous polymer matrix balloon infuse with flushing fluid so that whenthe burr is rotated, the infused polymer matrix leaks fluid and flushesthe ablated particulate into the aspiration sheath. Further, in thepresently preferred embodiment, the wire mesh 592 is a metal materialsuch as stainless steel. However, other materials such as polymers maybe used.

In some instances, it may be desirable to coat the outer surface of thepolymeric balloon with a hydrophilic coating such as Hydropass™,available from Boston Scientific and described in U.S. Pat. No.5,702,754. The hydrophilic coating attracts water molecules, therebymaking the surface slippery and easier to advance along the guidecatheter. In addition, the hydrophilic coating may be beneficial duringablation since less torque may be transferred to a vessel wall if theburr stalls. In addition, the differential cutting ability of the burrmay be enhanced due to the increased ability of the burr to slide oversoft tissues.

It will be appreciated by one of ordinary skill in the art that thepresently preferred embodiment may also be used in other surgicalprocedures such as percutaneous endarterectomy. Further, it will beappreciated that the ablation burr system may be used to ablate a newlumen through peripheral vasculatures or to remove occlusions fromRestenosis Stents.

While the preferred embodiments of the invention has been illustratedand described, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.The scope of the invention should therefore be determined from thefollowing claims and equivalents thereto.

1. A device for ablating an occlusion in a patient's vasculature,comprising: a rotary drive shaft; a drive source operatively connectedto the rotary drive shaft for rotating the rotary drive shaft; and anocclusion removal device secured to the rotary drive shaft for rotationtherewith, the occlusion removal device comprising a polymeric balloonsection, the polymeric balloon section being configured to expand in acontrolled manner between a first cross-sectional area and a secondlarger predetermined maximum cross-sectional area, wherein a portion ofthe balloon includes an abrasive exterior surface.
 2. The device ofclaim 1, wherein the polymeric balloon section includes means forcontrolling the expansion of the polymeric balloon section between thefirst cross-sectional area and the second larger cross-sectional area.3. The device of claim 1, wherein after the second largercross-sectional area is attained, the cross-sectional area of theballoon is independent of higher rotational speeds of the rotary driveshaft.
 4. A device for ablating an occlusion in a patient's vasculature,comprising: a rotary drive shaft; a drive source operatively connectedto the rotary drive shaft for rotating the rotary drive shaft; and anocclusion removal device secured to the rotary drive shaft for rotationtherewith, the occlusion removal device comprising a polymeric balloonsection, the polymeric balloon section being expandable in a controlledmanner between a first diameter and a second larger diameter uponrotation of the occlusion removal device, wherein a portion of theballoon includes an abrasive exterior surface.
 5. The device of claim 4,wherein the polymeric balloon section is an elastomeric balloon section.6. The device of claim 4, wherein the occlusion removal device includesmeans for controlling the expansion of the polymeric balloon sectionbetween the first diameter and the second larger diameter.
 7. The deviceof claim 6, wherein the polymeric balloon section includes the means forcontrolling the expansion of the polymeric balloon sections.
 8. Amedical device, comprising: a rotary drive shaft; a drive source thatrotates the rotary drive shaft at a selected speed measured inrevolutions per minute; and an occlusion removal device secured to therotary drive shaft for rotation therewith, the occlusion removal devicecomprising a polymeric balloon section, the polymeric balloon sectionbeing expandable in a controlled manner between a first cross-sectionalarea and a second larger cross-sectional area, wherein a portion of theballoon includes an abrasive exterior surface.
 9. The medical device ofclaim 8, further comprising means for controlling the expansion of thepolymeric balloon section between the first cross-sectional area and thesecond larger cross-sectional area.
 10. The device of claim 9, whereinthe occlusion removal device includes the means for controlling theexpansion of the polymeric balloon section.